By Anton Toloui, Sky Sports News

VAR makes its debut in English football this week after 18 months worth of trials and training.

Anton Toloui asks the questions to those in charge of the new Video Assistant Referee trial ahead of the system's debut in Monday's FA Cup third-round clash between Brighton and Crystal Palace.

When can video assistant referees (VAR) be used?

Only in four scenarios:

Awarding a goal

Deciding whether an offence is worthy of a direct red card

Awarding a penalty

Mistaken identity

It cannot be used for run-of-the-mill tackles anywhere outside the penalty area, for bookings or for free-kicks. Just huge, game-altering decisions.

Can VAR overrule a referee?

No. The on-field referee will have the final say on all decisions. He or she will watch an incident on a TV monitor at the side of the pitch and have the final decision. It's happened before where the VAR recommends one decision and the on-field official decides another.

So when will the VAR intervene?

The VAR and his team will review an incident if they feel it's either been missed or if there's "clear evidence of an error" by the on-field referee.

Referee Gianluca Rocchi needed to check with the Video Assistant Referee (VAR) during the Serie A match AS Roma vs Lazio on November 18,.

How will that work?

The VAR will speak to the on-field referee to let him or her know there's an incident that needs looking at. The referee will then go over to the pitchside monitor where the footage will be reviewed and discussed between the pair. The VAR will make a recommendation, it's up to the on-field referee to have the final say.

How will we know if an incident is being reviewed?

To be frank, we won't. The communications between the on-field at the VAR won't be broadcast, unlike in cricket and rugby union. This may change in the future but while the system is being trialled the authorities don't want to put more pressure on the officiating crew who are still learning.

So when would VAR have changed things?

A good example is the Premier League game between Brighton and Stoke in November. Ryan Shawcross brought down Glenn Murray in the penalty area but the view of referee Lee Mason was obstructed so no penalty was awarded. If the VAR system was in use then Mason would have been invited to review the footage and likely reversed his decision.

VAR was used in the Coppa Italia match between Juventus and Torino, which ended in controversy

VAR was used in the Coppa Italia match between Juventus and Torino, which ended in controversy

How long will a decision take?

It takes about 30-40 seconds on average for the VAR team to clip up and review a decision at the match centre. However, when it's not something as simple as an offside or multiple camera angles need to be viewed then by the time a referee has made a decision then up to three minutes could have passed.

Will VAR be a big weapon in the war against diving?

Probably not. Diving is tricky as if there's contact between two players it's difficult to prove a referee has made a "clear error". Take the incident involving Everton's Oumar Niasse at Crystal Palace earlier this season. The player went down in an exaggerated manner, which helped earn his side a penalty. There was, however, contact between him and the defender making the challenge, meaning the on-field decision would likely have stood. So there will still be a need for FA disciplinary bodies, who went on to ban Niasse for two games.

What about off-the-ball incidents?

This is where VAR could excel. A referee can't see everything but there are at least 12 cameras in use at every Premier League game so very little gets missed. If Ashley Young's elbow on Dusan Tadic happened in one of these VAR trial games this week it's likely the on-field referee would be alerted and when the ball next went dead he or she would review the footage and probably send the Manchester United full-back off.

Mike Riley will be overseeing the entire operation from the PL Match Centre.

Will it finally sort out the offside debate?

No, VAR will only be used for offsides if a goal is scored or in the build-up to a penalty. So if a player in an offside position has a chance that's saved by the goalkeeper and the ball goes out for a corner, VAR won't be used.

Will we see VAR very often?

According to the head of referees, about one in three matches that's had the VAR system has used video technology to aid the officials. Around 500 games have used a version of the system including in MLS, Serie A, Bundesliga and FIFA youth tournaments.

Will it become a permanent fixture in football?

We're still a fair while away from that. FA Cup and Carabao Cup matches will be closely monitored by the law's rulemaking body, the IFAB, before their AGM in March. We could feasibly see it introduced at the World Cup in Russia and the Premier League is keenly watching to see how successful the trials go from now until the end of the season.